The present invention relates generally to beam forming lenses used with antennas which scan electronically in azimuth and elevation, and more specifically to a planar microwave array lens.
Curved reflectors and lenses are both commonly used as collimating elements in high-gain, narrow beam microwave antennas. The choice between a reflector or lens for a given application depends upon many factors. For example, the Rotman lens is considered the optimum beamformer for producing time-delay steered beams over wide angles, but its requirement of a curved back face prohibits application to some problems, most notably those requiring large planar arrays. For a good description of the Rotman lens technology, see the discussion published in Rotman, W., and Turner, R. F. (1963) "Wide-angle microwave lens for line source applications", IEEE Trans. Antenna Propag., pp. 723-632, the disclosure of which is incorporated by reference.
Alternatives to the Rotman lens include curved wide-angle lenses and planar lenses. These lens systems are known in the art, and each possess advantages and disadvantages. For example, a planar lens (with a planar front surface which is parallel to a planar back surface) is incapable of wide-angle scanning, because the elements of the back face are normally placed directly behind the front face elements. Curved wide-angle lenses are heavy and expensive to build.
From the foregoing discussion, it is apparent that a scanning lens antenna which uses a planar lens, yet is capable of performing wide-angle scanning would be a welcome addition to the art of beamforming lens design. The present invention is intended to provide a new design which uses a planar lens, yet is capable of wide-angle scanning.